如果在不保持纵横比的情况下调整大小,则旋转 QGraphicsPixmapItem 会导致剪切 [英] Rotate QGraphicsPixmapItem results in shear if resizing without keeping aspect ratio
问题描述
我正在尝试旋转 QGraphicsPixmapItem
子项.对于其他 QGraphicsItem
,旋转和缩放工作正常.但是对于 QGraphicsPixmapItem
,如果尺寸不保持纵横比,我会得到剪切而不是旋转.
I am trying to rotate a QGraphicsPixmapItem
child. For other QGraphicsItem
, rotation and scaling work fine. But for a QGraphicsPixmapItem
, if the size does not keep aspect ratio, instead of rotation I get shear.
示例代码:
#include <QApplication>
#include <QGraphicsView>
#include <QMessageBox>
#include <QGraphicsPixmapItem>
#include <QFileDialog>
int main(int argc, char *argv[])
{
QGraphicsScene s;
s.setSceneRect(-200, -200, 500, 500);
QGraphicsView view(&s);
view.show();
QGraphicsPixmapItem p;
QString fileName = QFileDialog::getOpenFileName(0, QObject::tr("Open Image File"), QString(), QObject::tr("Png files (*.png);;Jpeg files (*.jpg *.jpeg);;Bitmap files (*.bmp)"));
p.setPixmap(QPixmap(fileName));
s.addItem(&p);
QMessageBox::information(0, "", "");
QTransform original = p.transform();
// scale aspect ratio then rotate
QTransform scalingTransform0(0.5, 0, 0, 0, 0.5, 0, 0, 0, 1);
// p.setTransformOriginPoint(p.boundingRect().center()); // doesn't help shear
p.setTransform(scalingTransform0 * original);
p.setRotation(20);
QMessageBox::information(0, "", "");
// scale
QTransform scalingTransform(0.5, 0, 0, 0, 1, 0, 0, 0, 1);
p.setTransform(scalingTransform * original);
QMessageBox::information(0, "", "");
// rotate
p.setRotation(20);
QMessageBox::information(0, "", "");
// unrotate then rotate again
p.setRotation(0);
QMessageBox::information(0, "", "");
QTransform rotTransform = p.transform().rotate(20);
p.setTransform(rotTransform);
// or p.rotate(20);
return app.exec();
}
结果:
对于QGraphicsPixmapItem
s,我不知道如何获得简单的旋转,没有剪切,并且项目必须记住旋转.
I don't know how to get simple rotation, without shearing, for QGraphicsPixmapItem
s, and the item must remember the rotation.
推荐答案
为什么 QGraphicsPixmapItem
表现如此不一致仍然是个谜.
It is still a mystery why QGraphicsPixmapItem
behaves so inconsistently.
解决办法:
缩放项目时,缩放像素图,将生成的像素图应用于项目.
在这种情况下,旋转将起作用(因为 QGraphicsPixmapItem
并没有真正缩放).
A solution:
When scaling the item, scale the pixmap, apply resulting pixmap to item.
In that case rotation will work (because QGraphicsPixmapItem
is not really scaled).
QPixmap p1 = pixmap.scaled(100, 100, Qt::IgnoreAspectRatio, Qt::SmoothTransformation);
p.setPixmap(p1);
p.setRotation(20);
这种方法会降低质量,所以我最终重新加载了文件
This approach loses quality, so I ended up reloading the file
QPixmap p1 = (QPixmap(fileName)).scaled(100, 100, Qt::IgnoreAspectRatio, Qt::SmoothTransformation);
p.setPixmap(p1);
p.setRotation(20);
如果有更好的解决方案,我很乐意看到.
If there is a better solution, I will be happy to see it.
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